Electronically controlled transmissions of motor vehicles are set by means of transmission actuators which receive electronic control signals and convert them into mechanical actuating positions. In this context, a plurality of actuators, usually pneumatically driven actuating pistons, are used for the gear speed, gate, split and range. In order to determine the travel position of an actuating piston which is used for one of the abovementioned functions, position sensors or travel sensors are used which specify the current position of the piston to an electronic evaluation unit. In this way, a control circuit is provided which receives a specific transmission position as a set point value and sets the transmission in accordance with the input signal.
Typical sensors which are used for this purpose are what are referred to as PLCD travel sensors (permanent magnetic-linear-contactless-displacement sensors). These known sensors are essentially composed of a soft magnetic core which is surrounded by a coil. A permanent magnet which is moved toward the sensor leads to a virtual division of the core. If a suitable alternating current is applied to the primary coil, a voltage which is dependent on the position of the permanent magnet is induced in the evaluation coils. The sensor is supplied with a suitable alternating current, and the signals are processed, evaluated and converted by electronics which are specially provided for this purpose.
Disadvantages of the known devices for setting a transmission are the complex spatial configuration and the connection equipment for connecting the electronic evaluation unit and the sensors to the electronic control unit. The long lines and the fact that the sensors are distributed over long distances entail an increased level of susceptibility to faults. Furthermore, mounting is costly and expensive.